netcode

Netcode is the set of software practices and protocols that enable multiplayer games to transmit data, stay synchronized, and feel responsive across a network. It covers state replication, input handling, prediction, reconciliation, and error correction to keep players in a consistent game world despite latency and packet loss.

A common architecture is a client–server model with an authoritative server. Clients send inputs to the server, the server simulates the world, and updates are broadcast back to clients. To reduce the sensation of latency, clients often perform prediction (instant locally simulated actions) and later reconcile their state with the authoritative server data.

Key techniques include:

- Client-side prediction: projecting local actions forward before server confirmation to feel responsive.

- Server reconciliation: correcting the client state when the server’s authoritative result differs.

- Interpolation: smoothing movement between received state updates to hide jitter.

- Extrapolation: predicting future states when updates lag, which can introduce errors.

- Lag compensation: methods to make actions feel fair despite latency, such as rewinding to the moment a hit occurred on the server.

- Rollback netcode: commonly used in fast-paced games (e.g., fighting games), where mispredictions trigger a quick rollback to a previous state and replay with corrected inputs to minimize visible stutter.

- Lockstep: used in certain genres (notably some real-time strategy games), requiring determinism and can be sensitive to latency.

Important considerations include tick rate and bandwidth, choice of protocol (UDP for real-time, with optional reliability layers; TCP is generally less used for motion-critical data), security and anti-cheat measures, and the balance between responsiveness and game state accuracy. Netcode design is heavily influenced by game genre, platform, and target player bases.